STATEN ISLAND, N.Y. --- The Port Richmond mother found dead alongside her four children in a bizarre murder-suicide in Port Richmond last week had soot in her lungs, meaning she was alive and breathing after her apartment was set ablaze, according to law enforcement sources.

That new bit of medical evidence, along with details that her 14-year-old son did not have any soot in his lungs, is leading investigators to believe that the mother, 32-year-old Leisa Jones, may have killed her children and then set their 302 Nicholas Ave. apartment ablaze.

Staten Island Advance/Hilton FloresNew medical evidence suggests Leisa Jones killed her children before setting fire to their apartment at 302 Nicholas Ave. Authorities say they may never know for certain who was responsible for the deaths.

The autopsies of the family also revealed that Ms. Jones did not have her throat slit by a straight razor, as her three older children did.

While the latest information adds more weight to the suggestion that Ms. Jones committed the unspeakable crimes, authorities — unlike in the early hours of the investigation — are not ready to label her the killer.

”You try to reach a conclusion because it’s essentially your job as an investigator to do that, and if we’re able to draw a conclusion on this case, we will,” Paul J. Browne, the chief spokesman for the New York Police Department, told the New York Times yesterday. “But it’s possible we never will.” Police had initially stated publicly that her 14-year-old son, C.J. Raymond, was the prime suspect in the case. Paul Browne, the NYPD’s deputy commissioner of public information, told reporters on Thursday afternoon that a straight razor was found underneath the boy, and said he had a history of starting fires.

Yesterday, law enforcement sources said that C.J., along with his sisters Melonie, 7, and Brittney, 10, did not suffer any smoke inhalation, which means they were not breathing when the fire was set.

The two girls died after their throats were slit, according to the city medical examiner’s office, while C.J.’s cause of death remains inconclusive pending further tests.

Ms. Jones’ cause of death is also pending further study, while her 2-year-old son Jermaine Sinclair, died from smoke inhalation at Richmond University Medical Center, West Brighton.

The NYPD said in a statement yesterday they still have made “no final determination as to who was responsible.”

Earlier yesterday, sources close to the investigation told the Advance that both Ms. Jones and C.J. had ingested some type of drug before dying. It was unclear what type of drug, but pills were found in their stomachs during an autopsy.

On Sunday, Browne told reporters that investigators believe Ms. Jones wrote a badly burned note found in the apartment with the words “am sorry.” The handwriting matched a diary found in the apartment also believed to have been written by Ms. Jones.

Ms. Jones, a single mother with children by several different fathers, had been attending beauty school while working part-time as a security guard at the Macy’s in the Staten Island Mall to make ends meet. She had been evicted from her Washington, D.C., apartment, and her landlord in Port Richmond sued her in February for almost $7,000 in back rent, court documents show.

C.J. reportedly had psychological problems that spurred city school officials to try to transfer him into a special district for severely disabled students.